program square;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  i: integer;
  s: real;
  x, y: array [1..3] of integer;

begin
  for i:=1 to 3 do
  begin
    readln(x[i]);
    readln(y[i]);
  end;

  s:=abs((x[1]*y[2]-x[2]*y[1])+(x[2]*y[3]-x[3]*y[2])+(x[3]*y[1]-x[1]*y[3]))/2;
  writeln(s:0:1);
  readln;
end.
